Qt-Interface For Volume Visualization

Practical Course Computer Graphics For Advanced Supervising

Dr. Susanne Krömker

Stefan Becker & Ronald Lautenschläger

Outline1. Terms you should know2. Comparison of GUI Designers3. QtOpenGL Module4. Callback methods5. Threads6. Qt vs. GTK+ (overview)7. Boy‘s Surface8. QTvvis9. Problems during porting10. Summary11. Sources

OpenGL [Wikipedia]• OpenGL (Open Graphics Library) is a

specification defining a cross-language cross-platform API for writing applications that produce 3D and 2D computer graphics – Interface of over 250 different function calls– competes with Direct3D on Microsoft Windows

platforms– widely used in CAD, virtual reality, scientific

visualization, information visualization, and video game development.

GTK(MM) [Wikipedia]

• C++ interface for the GUI library GTK+ • typesafe callbacks • widgets extensible via inheritance• You can create user interfaces either in

code or with the Glade Interface Designer, using libglademm

• gtkmm is free software distributed under the GNU Library General Public License (LGPL)

Qt [Wikipedia]

– Cross-platform graphical widget toolkit for the development of GUI programs

– Produced by the Norwegian company Trolltech– Qt uses an extended version of the C++ programming

language – Bindings exist for Python, Ruby, C, Perl and Pascal– It runs on all major platforms– Features

• SQL database access• XML parsing• thread management

Platforms:• Qt/X11 — Qt for X Window System • Qt/Mac — Qt for Apple Mac OS X • Qt/Windows — Qt for Microsoft Windows • Qt/Embedded — Qt for embedded platforms (PDA,

Smartphone, ...) • Qt Console — edition for non-GUI development • Qt Desktop Light — entry level GUI edition, stripped of

network and database support• Qt Desktop — complete edition • Qt Open Source Edition — complete edition, for open-

source development

Qt [Wikipedia]

Qt - Elements• QtCore — Core Classes used by other Qt-Modules • QtGui — Component for GUI creation • QtOpenGL — OpenGL support• QtDesigner — Qt-Designers extension classes • Qt3Support — Special classes to ensure compatibility

to Qt 3 • qmake — generator for makefiles• moc — creates meta-information of classes used in

program• uic — creates c++ code from UI-Classes • rcc — resource-Compiler

Qt - Hierarchy

• QObject– Base class of all Qt-Objects

• QWidget – Inherits from QObject– Base class of all Widgets

Glade Interface Designer

• Glade Interface Designer is a graphical user interface creator for GTK+

• programming language–independent• does not produce code for events• created XML file, and optionally one or

more C programming language files into which programmers insert their code.

• free software, distributed under the GNU General Public License

Glade Interface Designer

XML Glade-GUI description example:<?xml version="1.0" standalone="no"?> <!--*- mode: xml -*--><!DOCTYPE glade-interface SYSTEM "http://glade.gnome.org/glade-2.0.dtd">

<glade-interface>

<widget class="GtkWindow" id="windowToVrend"> <property name="title" translatable="yes">window1</property> <property name="type">GTK_WINDOW_TOPLEVEL</property>... <property name="skip_pager_hint">False</property> <property name="type_hint">GDK_WINDOW_TYPE_HINT_NORMAL</property>...

<child> <widget class="GtkVBox" id="vboxToVrend"> <property name="visible">True</property>...

<child><widget class="GtkLabel" id="labelTitle"> <property name="visible">True</property> <property name="label" translatable="yes">&lt;b&gt;convert to Vrend&lt;/b&gt;</property>

... <property name="width_chars">-1</property> <property name="single_line_mode">False</property> <property name="angle">0</property></widget>

...

Short Demo Qt-Designer

XML-GUI Description created by Qt-Designer

<ui version="4.0" > <author></author> <comment></comment> <exportmacro></exportmacro> <class>CDialogAbout</class> <widget class="QDialog" name="CDialogAbout" > <property name="geometry" > <rect> <x>0</x> <y>0</y> <width>337</width> <height>423</height> </rect> </property> <property name="minimumSize" > <size> <width>337</width> <height>423</height> </size> </property>…<property name="baseSize" ><pixmapfunction></pixmapfunction> <resources/> <connections/></ui>

Qt-Designerembedding UI file

1. Compile ui file created by Qt Designer with UIC (Compiler for ui-classes/files)

2. Usage (example)– In your Ui-Folder:

uic – o TargetFileName.h UiFileName.ui– Include compiled header file in your cpp or header

file#include <TargetFileName.h>

– Create reference to objects of namespace Uiprivate:

Ui::TargetFileName ui;– In cpp you have to setup the generated form like

thisui.setupUI(this);

QtOpenGL Module

• QGLColormap– custom colormaps for QGLWidgets

• QGLContext– OpenGL rendering context

• QGLFormat– display format of OpenGL rendering context

• QGLWidget – widget for rendering OpenGL graphics

QtOpenGL Module

• QGLWidget– initializeGl()– paintEvent()– resizeGl()– swapBuffers()– QGLFormat format()

• Rertuns GLContext

QtOpenGL Module

• How to display OpenGL within a Qt window

1. Your class needs to inherit from QGLWidget• Classname : public QGLWidget

2. Initialization in cpp• Classname( QGLFormat format, QWidget*

parent )

QtOpenGL Module

• QGLFormat – specifies the display format of an OpenGL

rendering context– Methods:

• depth(), doubleBuffer(), setRgba() etc…

• GtkGlContext–Glib::RefPtr<Gdk::GL::Config>

&refGLConfig

Gtk::GL::DrawingArea

• GTK+ DrawingArea widget supports OpenGL rendering

• Your class needs to inherit from Gtk::GL::DrawingArea

• Initialization– set_gl_capability( refGLConfig )

Callback-Methods Introduction

• Defines behaviour of program– A method which is passed to another by

argument and is executed at certain conditions

Callback-Methods

• Libsigc++ :– Implements typesafe callback system for C++– Signals and slots– Uses Callback-Mechanism. The programmer

passes the adress of a method to another which can execute the method behind the adress

Qt – Signals & Slots

• Signals / Slot mechanism– Communication between objects of the

program– Alternative to callbacks

Qt – Signals & Slots#include <QObject> class Number : public QObject {

Q_OBJECTprivate:

int _value;public:

Number() { _ value = 0; }int value() const { return _value; }

public slots: void setValue( int value) {

if( value != _value ) {

_value = value; emit valueChanged ( value );

} }

signals: void valueChanged( int new Value);

};

Qt – Signals & Slots

Number a, b;

QObject::connect(&a, SIGNAL(valueChanged(int)), &b, SLOT(setValue(int)));

a.setValue(12); // a.value() == 12// b.value() == 12 because signal of a is connected b.setValue(48); // a.value() == 12 because signal of b is not connected // b.value() == 48

Comparison

• Libsigc++– Signal is connected to method that should

be invoked– Easy callback mechanism

• Qt Signals & Slots– Easy mechanism– signal is connected to slot

• When signal is emitted the connected slot is invoked

Threads

• Definition– A way for a program to split itself – A thread can be executed parallel with

other threads – Used for heavy computation processes

for example:• Rendering and event processing at the

same time

Glib::ThreadDeclaration in header:

Glib::Thread *m_pThread;Implementation in sourcefile:m_pThread = Glib::Thread::create(

sigc::mem_fun(*this, &ClassName::doSomething()), true);

Easy creation of thread

QThread• Declaration: 

class MyThread : public QThread{public:

void run();};

Implementation:void MyThread::run(){

doSomething();exec();

}• No possibility to create thread without creating new class deriving

from QThread

QCoreApplication::processEvents

• Alternative to dispense with QThread• Processes all events of Qt application for time of

invocation• This function is called normally when program is busy

performing a long operation i.e.– Converting– Rendering– Opening file– etc.Otherwise application would freeze

Thread comparison

• Glib::Thread– Easy to use– Use Glib::Thread::create() to instanciate your thread

and simply connect it to destination method of any object

• QThread– Precondition is creation circumstantially of new

class that inherits from QThread– QThreads can “talk with each other” by connection

of signals and slots– QThreads share data with all other threads within

the process

Qt vs. GTK+ (overview)

Glade (has poorer documentation)

Has good RAD Tool (rely on Qt Designer and KDevelop)

IDE

Java, Perl, Python and many more

Perl, PHP, Python Language Bindings

Based on CBased on C++Programming Language

http://www.gtk.orghttp://www.trolltech.comWeb Site

GTK+QtWeb Site

Qt vs. GTK+ (overview)

Less functionality (needs many other libraries like libsigc++ for signals i.e.)

Qt Toolkit everything is included Usage

Needs separate project like gnome-db

Has integrated data-aware widget

Database

Developer has to embed his own scripting language (Python, LUA…)

Has internal support for scripting (QAS)

Scripting

Mainly developed for Linux, ports for Win32, DirectFB, BeOS are available, Macintosh in development (far from complete)

Runs on Linux, Windows, Macintosh

Supported OS

GTK+QtWeb Site

Qt vs. GTK+ (overview)

GTK is freeware, GNU LGPL Qt is only freeware on Linux and for open source projects

License

Comprehensive reference (most time behind API documentation) many source codes from GTK Team

Very good documentation and many source codes from Qt and KDE Team

Documentation

Talks via CORBA Talks via DCOP with other Qt Apps

Communication

GTK+QtWeb Site

Qt vs. GTK+ (overview)

Win32 Port unstable, Macintosh version far from completion

•Huge sources and binaries. Takes ages to compile•Objects not referred by namespace but simple literal prefix “Q”

Weaknesses

•Internationalization features (Unicode etc.)•gtkmm: Good namespaces•gtkmm: well defined, clean, modular API

•Integrated internationalization and translation featuresMany helpful tools bundled•RAD Tools with nice wizards•Many advanced widgets available

Strengths & Features

GTK+QtWeb Site

Boy’s Surface

• Seminar talk of Babett Lemke

• Author: Dr. Susanne Kroemker

• Tasks:– Porting the program

Boy's Surface from Linux to Win & Mac

– Replacing the GLUT-Gui with Qt

Boy's Surface

• Short DemoBoy's Surface with Qt

Boy's SurfaceWhat is GLUT ?

OpenGL Utility Toolkit (GLUT) • library of utilities for OpenGL programs• Routines for drawing a number of geometric

primitives (both in solid and wireframe mode) are also provided

• limited support for creating pop-up windows• At the moment no further development of GLUT

Boy's Surface

• Startwindow

Boy's Surface

• Mainwindow

QTvvis

• Original Programm (GTK+ Version) byJohannes Lampel & Tobias Eberlehttp://vvis.sourceforge.net

QTvvisWhat is vvis ?

• vvis renders 3D scalar fields like volume data

• Several file formats like OpenQvis or VRend are supported

• Supports TiFF conversion

Demo QTvvis

QTvvis (Qt-Port)

• Requirements:– Qt 4.1.1 at least for compiling– OpenGL libraries ( Windows )– Libtiff library ( Win, Mac, Linux )

Problems during porting

• No QGLWidget in Qt-Designer (opensource edition)

• Layouting had to be done manually

Problems during porting– QThreads

• No possibility to create a thread without creating new class deriving from QThread in Qt

– Vector and QWidgets• QWidgets have private constructor and aren’t

storable into vector. Solution: Store reference– Data type conversion

• For example: std:String to QString– QString string = std_string.c_str();

Problems during porting– Documentation

• GTK+, GLib has poor Html documentation. Time-consuming search for all libraries documentation

– Installation of vvis• Research on Linux (no prev. knowledge existed)• vvis has many requirements (difficult installation)• At the beginning porting based on screenshots

because original version wasn’t possible to run– In general

• Only little knowledge of Qt, C++ existed• No software development knowledge of Macintosh

OS and Linux

Summary• QT Support

– Qt 4.1.1 has to be installed (due to bugs in previous versions)– Qt 4.x is not fully compatible with Qt 3.x

• Special classes must be implemented if you want QT3 support – But: Qt 4 will soon be standard on all Linux distributions– Qt is still in development and some control elements doesn’t work

properly on all platforms

• Porting of a GTK+ Application– GTK+ and Qt functionalities are comparable – Complexity should not be underestimated!

• Hope to enhance acceptance of vvis through:– Simple installation. vvis requires gtk(mm), glib, pango, atk, libsigc++,

libglade, gtkglext(mm)– Less cost of configuration

Sources• Wikipedia http://www.wikipedia.org• vvis.net http://vvis.sourceforge.net• Trolltech http://doc.trolltech.com• Trolltech List Archives http://lists.trolltech.com/qt-interest/• Trolltech Bug Tracking list

http://www.trolltech.com/developer/tasktracker.html?method=entry&id=95340• GTK+ API Description http://www.gtk.org/api/• GTKMM, GLIB Documentation http://www.gtkmm.org

/docs/• GTKMM List Archive http://

mail.gnome.org/archives/gtkmm-list/

Sources• OpenGL Framebuffer Description

http://www.delphi3d.net/articles/viewarticle.php?article=framebuf.htm

• OpenGL Texture Tutorial http://www.nullterminator.net/gltexture.html • Delphi OpenGL Wiki http://wiki.delphigl.com/index.php/Hauptseite• GluSphere Example Source code

http://www.et.byu.edu/~merk/me570/qtRed/qtmaterial.cpp• Libsigc++ 2 documentation http://libsigc.sf.net/libsigc2/docs/• GTK+ for Mac• http://developer.imendio.com/wiki/Gtk_Mac_OS_X/Things_to_do• GTK+ vs. Qt• http://mail.gnome.org/archives/gtk-list/2003-

November/msg00037.html• Freshmeat: GTK+ vs. Qt• http://freshmeat.net/articles/view/928/